Axial pistons hydraulic pump able to function in one or the other rotating direction

ABSTRACT

A hydraulic pump able to function in one or the other rotating direction is of the type including a rotating barrel bearing pistons applied against a valve plate provided with two symmetrical opposed drillings. The valve plate provided with two symmetrical and opposed drillings, one connected to one of the output openings of the pump, the other one connected to the other output opening, is jointly linked to a double piston having two sections of equal surfaces, one of these surfaces being connected with one of the two output openings, the other one being connected with the other output opening so that valve plate is always applied against barrel bearing pistons by the discharge pressure in any rotating direction of the pump.

The present invention is concerning an axial pistons hydraulic pump and more particularly such a pump having a small or very small cubic cm displacement and able to function in one or the other rotating direction in order to feed an hydraulic receptor in one way or the other.

It is necessary to have the possibility to activate, for instance within a petrol drilling tube a double action hydraulic jack without to be obliged to use an hydraulic distributor while placing the pump in a very small volume.

To do this it is advantageous to use the swash plate and axial pistons pump technology.

The swash plate and axial pistons pumps are known since a long time.

Particularly it is known to use hollow pistons resting against a swash or wobble plate by means of sliding skids through which each pistons is fed with hydraulic liquid when its sliding skid runs over a curved groove, hereafter called lunula, carved on the surface of the swash plate; the discharge of the hydraulic liquid sucked inside the hollow piston passing through a one way valve placed at the end of the cylinder inside which the piston is reciprocating.

It is known to use with that kind of pump what is known as a valve plate distribution, the pistons being inside a rotating barrel whose back side is pressed by a spring against the valve plate made of a disc provided with arcuate drillings.

However it appears that this technology, widely used by the applicant, does not fit for pumps whose cubic cm displacement is lower than 4 to 5 cm3, because in such cases, to prevent the back face of the barrel to be separated from the valve plate by the delivery pressure it is necessary to provide said lunulas with an area so small that it is impossible to machine them. In addition, the very small dimensions of the lunulas has for effect that the pump input is considerably reduced which is not compatible with the intended use of the pump.

The object of the present invention is to bring a solution to this problem.

Said solution consists in a swash plate hydraulic pump able to function in both rotating directions of the kind of pump comprising a rotating barrel carrying the pistons, said barrel being pressed against a valve plate provided with two symmetrical and opposed drillings wherein said valve plate provided with two symmetrical and opposed drillings one connected with one of the output openings of the pump, the other with the other output opening is jointly linked to a double piston having two sections of equal surfaces, one of these surfaces being connected with one of the output openings of the pump, the other surface being connected with the other output opening; so that said valve plate is constantly pressed against the barrel carrying the pistons by the output pressure whatever the sense of rotation of the pump, this permitting to manufacture a small cubic cm displacement pump (particularly lower than 4 to 5 cm3) in which said symmetrical drillings have small dimensions and in which the output pressure cannot separate the barrel from the valve plate.

Preferably the spherical heads of the pistons are maintained against the canted face of the swash plate by a disc acted by the spring applying the barrel against the valve plate.

The invention may be carried into practice in various ways and one embodiment will be described by way of example with reference to the accompanying drawing of which:

FIG. 1 is a longitudinal section of a known swash pump with a valve plate.

FIG. 2 is a plan view of the FIG. 1 valve plate with its two symmetrical lunulas at a slightly larger scale.

FIG. 3 is a longitudinal section of an example of embodiment of a pump having a cubic cm displacement lower than 4 to 5 cm3 able to discharge hydraulic fluid in both rotating directions.

FIG. 4 is a plan view of the valve plate of a known pump with its two lunulas whose dimensions should be determined for the pump to have a cubic cm displacement lower than 4 to 5 cm3.

FIG. 1 is showing a known pump comprising a shaft 1, driving a barrel 2 inside which are reciprocating several hollow pistons 3 resting against a canted plate or swash plate 4 by means of sliding skids 5.

The back side of barrel 2 is urged by a spring 9 against a disc 8 comprising two arcuate drillings 7/7′ hereafter called lunulas.

Hydraulic liquid is drawn in the pistons through one of the lunulas and discharged through the other one.

A groove 17 carved onto the surface of disc 8 allows each lunula 7/7′ to communicate with inside space 18 of the pump housing.

Opening 10 of the pump is intake opening when pump is rotating clockwise, opening 11 being discharge opening and reversely when pump is rotating anticlockwise.

Such a device is known.

It is known that it is necessary to balance hydrostatically the pump in order to prevent that the discharge pressure which creeps between the back face of the barrel and disc 8 separates them.

FIG. 2 illustrates that the interior space of each lunula may be schematically divided into three zones: a central zone 7 a; an external zone 7 c and a medium zone 7 b.

Inside zone 7 a the pressure is the discharge pressure P; in zone 7 c the pressure is null or equal to the pressure into the housing of the pump; in zone 7 b varies from P to 0 or to the pressure inside the housing of the pump.

If S is the surface of zone 7 a; dS the surface of zone 7 b, called resting surface; s the pistons surface and n the number of pistons under pressure, the following formula must be applied : P×(S+dS) lower than P×s×n.

For cubic cm displacement lower than about 4 to 5 cm3 piston diameter is about 6 to 8 mm.

When the above formula is applied in order to calculate surfaces S and dS the result is very small surfaces. FIG. 4 illustrates what is to be obtained, To get this inventor has created two artificial surfaces constituted by the double piston 81/82 which press upon valve plate 80. Such artificial pressure is balanced by increasing the surface of lunulas 70/70′.

FIG. 3 shows an embodiment of the present invention. Barrel 20 bearing pistons 30 is jointly linked to driving shaft 10. Pistons 30 are resting against swash plate 40 by means of sliding skids 50. Spring 90 is maintaining on one part piston heads against sliding skids 50 by means of disc 91 and on other part back side 21 of barrel 20 against valve plate 80 said valve plate 80 comprising two symmetrical circular drillings 70/70′.

Valve plate 80 is supported by a staged double piston the two sections 81 and 82 of which have equal surfaces on the side opposed to the drilling 70 and 70′, designated by S1 and S2. Piston 82 is sliding into a cylindrical chamber 31 which is connected to circular drilling 70 by conduct 84; while piston 81 is sliding into cylindrical chamber 32 which is connected to circular drilling 70′ by conduct 83. Chamber 31 within which piston 81 is sliding is connected to opening 11; while chamber 32 within which piston 82 is sliding is connected to opening 10.

Then, when pump is rotating in a sense for which the liquid under pressure is discharged through circular drilling 70 and opening 10, valve plate 80 is applied against back side 21 of barrel 20 by piston 82 urged by the discharge pressure. When pump is rotating in the other sense, liquid under pressure is discharged through circular drilling 70′ and opening 11 and valve plate 80 is applied against back side 21 of barrel 20 by piston 81 urged by the discharge pressure.

Because of these means it is possible to give a relatively large section to drillings 70 and 70′ without to be obliged to machine a valve plate such as illustrated on FIG. 4.

While the above invention has been described in liaison with a particular embodiment it is evident that it is not limited to that particular example and is comprising all technical equivalents and their combinations when they are within the scope of the invention.

Use of verbs such as “comprising”,” comporting or “including” and their combinations does not exclude other elements or steps other than those enumerated in the claims. Use of indefinite article “one” for an element does not exclude, unless specifically mentioned, presence of a plurality of such elements.

In the claims any reference number must not be interpreted as a limitation of the claim. 

1. An hydraulic pump able to function in one or the other rotating direction of the type comprising a rotating barrel bearing pistons applied against a valve plate provided with two symmetrical opposed drillings wherein said valve plate (80) provided with two symmetrical and opposed drillings (70,70′), one connected to one of the output openings (10) of the pump, the other one connected to the other output opening (11) is jointly linked to a double piston having two sections (81,82) of equal surfaces, one of these surfaces being connected with one of the two output openings (10), the other one being connected with the other output opening (11) so that the valve plate (80) is always applied against the rotating barrel (20) bearing the pistons (30) by the discharge pressure in any rotating direction of the pump.
 2. An hydraulic pump according to claim 1 wherein the spherical heads of the pistons (30) are maintained applied against the inclined plane of the swash plate (40) by means of a disc (91) pressed by a spring (90) which is applying said barrel (20) against said valve plate (80).
 3. An hydraulic pump according to claim 2 wherein said spring (90) is maintaining a back side of the barrel (20) against the valve plate (80).
 4. An hydraulic pump according to claim 1 wherein said valve plate (80) is provided with two symmetrical drillings (70,70′).
 5. An hydraulic pump according to claim 1 wherein the cubic displacement of the pump is lower than 5 cm3.
 6. An hydraulic pump according to claim 2 wherein said valve plate (80) is provided with two symmetrical drillings (70,70′).
 7. An hydraulic pump according to claim 3 wherein said valve plate (80) is provided with two symmetrical drillings (70,70′).
 8. An hydraulic pump according to claim 2 wherein the cubic displacement of the pump is lower than 5 cm3.
 9. An hydraulic pump according to claim 3 wherein the cubic displacement of the pump is lower than 5 cm3.
 10. An hydraulic pump according to claim 4 wherein the cubic displacement of the pump is lower than 5 cm3. 